1. Field of the Invention
The present invention relates to an active matrix EL display device using a current-driven light emitting element.
2. Description of the Related Art
Organic EL display devices using self light emitting organic electroluminescence (EL) elements do not require a backlight and have no limitation in their viewing angle, and therefore have been developed as a next-generation EL display device.
An organic EL element is a current-driven light emitting element that controls its luminance based on an amount of current flow. In recent years, active matrix organic EL display devices that include a drive transistor for each pixel circuit and drive an organic EL element have become the mainstream.
The drive transistor and its peripheral circuits are typically configured by thin-film transistors using polysilicon, amorphous silicon, or the like. Thin-film transistors are suitable for a large-sized organic EL display device, as it is easy to increase the size and the cost is low while having a weakness that variations in mobility and threshold voltages are large.
Further, designs of pixel circuits in order to overcome the variation and a chronological change in threshold voltages that are the weaknesses of thin-film transistors have been studied. For example, Unexamined Japanese Patent Publication No. 2009-169145 discloses an organic EL display device having a function of correcting a threshold voltage of a drive transistor and a method of driving this organic EL display device. Further, Unexamined Japanese Patent Publication No. 2002-134169 discloses an EL display device including a memory storing a gain and an offset of a luminance-voltage characteristic for each of pixels, and a correction circuit that corrects an image signal based on the data in the memory, wherein irregularity in luminance due to a luminance variation among pixels is reduced.